1. Field of the Invention
The present invention relates to a liquid jet recording head for jetting liquid to form flying droplets for recording on a medium.
2. Description of the Prior Art
A liquid jet recorder records by discharging liquid such as ink from a nozzle of a recording head. This type of recorder is attractive because noise generated during recording is negligibly low, the recorder attains high speed recording and the recording can be made on a plain paper without special treatment.
Among others, the liquid jet recording methods disclosed in Japanese Patent Application Laid-Open No. 51875/1979 and West Germany DOLS 2843064 are unique compared with other liquid jet recording methods because thermal energy is applied to the liquid to produce a motive force for discharging droplets.
In disclosed recording method, the thermal energy causes a rapid increase of volume in the liquid. Liquid is thus discharged from an orifice at an end of a recording head by the force due to this change in state forming flying droplets. The droplets are then deposited on a recording medium to form a record.
The liquid jet recording method disclosed in the West Germany DOLS 2843064, may be applied to a drop-on demand type recording method or a fall line type method having a high density multi-orifice recording head. Hence, it enables rapid formation of a high resolution and high quality image.
The recording head used in the above recording method comprises a liquid discharge unit including an orifice for discharging liquid, a liquid flow path having a heating unit by which a thermal energy for discharging droplets is applied to the liquid, and an electro-thermal converter for generating the thermal energy.
In a prior art recorder having a liquid jet recording head, wiring for the recording head extends across a substrate to a flexible wiring cable connecting the recording head to a drive circuit which produces an electrical signal to drive the electro-thermal converter of the recording head. The connecting pads of the flexible cable, for applying the electrical signal to the recording head, conventionally has been connected to wiring pads of the recording head by a press-contact method, a wire bonding method, soldering or by thermal a press-contact method. The flexible cable is then fixed to the recording head.
The substrate of the liquid jet recording head has one of a number of different wiring and heat generating resistor patterns depending on an the desired end product, e.g. eight lines with 2.5 lines/mm for a desk top calculator printer or sixteen lines with 4 lines/mm for a facsimile machine.
FIG. 1 shows a structure of a prior art liquid jet recording head. Numeral 1 denotes substrate, numeral 2 denotes electrodes through which electrical signals are supplied, numeral 3 denotes heat generating resistors which are electro-thermal converters, numeral 4 denotes an area of a protection film which protects the electrodes and the heat generating resistors from liquid, and numeral 5 denotes a flexible cable for connecting the substrate to a drive circuit.
In the prior art liquid jet recording head, the wiring area 6 is large and hence the quantity of the substrate material required for each head is large. Since the substrate material is made of an expensive material such as Si, the increase of the cost of the recording head due to this area of substrate is not negligible.
The excessive size of the substrate due to this unnecessary area reduces the efficiency of the etching, sputtering or vapor deposition process and impedes mass-production.
Further, because the mask used in production changes from product to product, the etching, sputtering or vapor deposition process becomes complex and the yield is lowered due to misoperation.
Still further, short-circuiting and bridging of the wiring occur with the same probability throughout the substrate area. Thus, the unnecessary area causes a reduction of the yield.
In a proposed liquid jet recording head, a substrate area having the heat generating resistors formed therein is separated from the substrate on which the recording head is formed and the major electrodes of the separate substrate and the electrodes of the recording head are electrically connected. The electrical connection of the recording head (discharge element) and the major electrodes (external wiring unit) is illustrated in FIGS. 2 and 3.
Numeral 7 denotes the discharge element. A liquid chamber 8 is fixed to a side of the discharge element 7 and a plurality of orifices 9 for the liquid are formed in the liquid chamber 8. Heat generating elements 11 are formed on a side of the discharge element facing a substrate 10 opposite the orifices 9. Numeral 12 denotes lead electrodes for supplying a current to each heat generating element 11.
The discharge element 7 is mounted on a substrate 14 of an external wiring unit 13 the electrodes 15 on the substrate 14 and the lead electrodes 12 are wire-bonded by wires 16. The bonding is sealed by sealing agent 17 to enhance reliability.
This structure, however, raises the following problem.
In order to improve the print quality in the liquid jet recording head, it is necessary to reduce the spacing between the orifices 9 and the recording paper. However, since the sealing agent 17 projects from the orifice plane, the spacing between the orifice plane and the recording paper cannot be reduced.
Further, as the spacing between the orifice plane and the recording paper is reduced, the sealing agent 17 rubs against the recorded paper, lowering the print quality. Alternatively, the sealing agent 17 is worn by the recording paper and the reliability of the sealing agent 17 and the reliability of the connecting area are lowered.